In today's radio communications networks a number of different technologies are used, such as Long Term Evolution (LTE), LTE-Advanced, Wideband Code Division Multiple Access (WCDMA), Global System for Mobile communications/Enhanced Data rate for GSM Evolution (GSM/EDGE), Worldwide Interoperability for Microwave Access (WiMax), or Ultra Mobile Broadband (UMB), just to mention a few possible technologies. A radio communications network comprises radio base stations providing radio coverage over at least one respective geographical area forming a cell. User equipments (UE) are served in the cells by the respective radio base station and are communicating with respective radio base station. The user equipments transmit data over an air interface to the radio base stations in uplink (UL) transmissions and the radio base stations transmit data to the user equipments in downlink (DL) transmissions.
Recently two main trends have emerged in the cellular telephony business. First mobile broadband traffic is more or less exploding in the e.g. WCDMA networks. The technical consequence is a corresponding steep increase of the interference in these networks, or equivalently, a steep increase of the load. This makes it important to exploit the load headroom that is left in the most efficient way. Secondly, radio communications networks are becoming more heterogeneous, with macro radio base stations being supported by micro radio base stations at traffic hot spots. Furthermore, WCDMA home base stations, also called femto radio base stations, are emerging in many networks. This trend clearly puts increasing demands on inter-cell interference management.
Below it is described the measurement and estimation techniques, needed to measure the instantaneous total load, also referred to as the received total power value, on the uplink air interface. It is e.g. shown in prior art that the load at the antenna connector is given by the noise rise, or rise over thermal, RoT(t), defined by
                                          RoT            ⁡                          (              t              )                                =                                                    P                RTWP                            ⁡                              (                t                )                                                                    P                N                            ⁡                              (                t                )                                                    ,                            (                  eq          .                                          ⁢          1                )            where PN(t) is the thermal noise level as measured at the antenna connector, also referred to as noise floor level and where PRTWP(t) is the total power value. This relative measure is unaffected of any de-spreading applied. The definition used for the total power value used here is simply the received total power value called received total wideband power
                                                        P              RTWP                        ⁡                          (              t              )                                =                                                    ∑                                  k                  =                  1                                K                            ⁢                                                          ⁢                                                P                  k                                ⁡                                  (                  t                  )                                                      +                                          P                neighbor                            ⁡                              (                t                )                                      +                                          P                N                            ⁡                              (                t                )                                                    ,                            (                  eq          .                                          ⁢          2                )            also measured at the antenna connector. Here Pk(t) is the power from the load in the own cell and Pneighbor(t) denotes the power as received from neighbour cells of the WCDMA system referred to herein as neighbour cell interference value. As will be seen below, a major difficulty of any RoT estimation algorithm is to separate the noise floor level PN(t) from the neighbour cell interference value Pneighbor(t).
Another specific problem that needs to be addressed is that the signal reference points are, by definition at the antenna connectors. The measurements are however obtained after the analogue signal conditioning chain, in the digital receiver. The analogue signal conditioning chain does introduce a scale factor error, γ(t), of about 1 dB that is difficult to compensate for. Fortunately, all powers of (eq. 2) are equally affected by the scale factor error γ(t) so when (eq. 1) is calculated, the scale factor error γ(t) is cancelled as
                                          RoT                          Digital              ⁢                                                          ⁢              Receiver                                ⁡                      (            t            )                          =                                                            P                RTWP                                  Digital                  ⁢                                                                          ⁢                  Receiver                                            ⁡                              (                t                )                                                                    P                N                                  Digital                  ⁢                                                                          ⁢                  Receiver                                            ⁡                              (                t                )                                              =                                                                      γ                  ⁡                                      (                    t                    )                                                  ⁢                                                      P                    RTWP                    Antenna                                    ⁡                                      (                    t                    )                                                                                                γ                  ⁡                                      (                    t                    )                                                  ⁢                                                      P                    N                    Antenna                                    ⁡                                      (                    t                    )                                                                        =                                                            RoT                  Antenna                                ⁡                                  (                  t                  )                                            .                                                          (                  eq          .                                          ⁢          3                )            In order to understand the fundamental problem of the neighbour cell interference value when performing load estimation, note thatPneighbor(t)+PN(t)=E└Pneighbor(t)┘+E[PN(t)]+ΔPneighbor(t)+ΔPN(t),  eq. 4)where E[ ] denotes mathematical expectation and where Δ denotes the variation around the mean. Since there are no measurements available in the radio base station that are related to the neighbour cell interference value, a linear filtering operation can at best estimate the sum E└Pneighbor(t)┘+E[PN(t)]. This estimate cannot be used to deduce the value of E[PN(t)]. The situation is the same as when the sum of two numbers is available. Then there is no way to figure out the values of the individual numbers.
In the 3rd Generation Partnership Project (3GPP) release 99, also called 3G systems, the Radio Network Controller (RNC) controls resources and user mobility. Resource control in this framework means admission control, congestion control, channel switching, and/or roughly changing the data rate of a connection. Furthermore, a dedicated connection is carried over a Dedicated Channel (DCH), which is realized as a Dedicated Physical Control Channel (DPCCH) and a Dedicated Physical Data Channel (DPDCH). In the evolved third generation (3G) standards, the trend is to decentralize decision making, and in particular the control over the short term data rate of the user connection. The uplink data is then allocated to an Enhanced-DCH (E-DCH), which is realized as the triplet: a DPCCH, which is continuous, an E-DCH (E)-DPCCH for data control and an E-DCH (E)-DPDCH for data. The two latter are only transmitted when there is uplink data to send. Hence the uplink scheduler of the radio base station determines which transport formats each user can use over E-DPDCH. The RNC is however still responsible for admission control, the only way to control R99 traffic. Today the scheduling and admission control in the radio communications network are not performing in an optimal manner resulting in a reduced performance of the radio communications network. For scheduling in the radio base station, there is no available low complexity neighbour cell interference estimation technology. The available technology requires measurement and subsequent optimal filtering of all user equipment powers in the UL. That is very costly computationally, and requires Kalman filters of high order for processing the measurements to obtain estimates of the neighbour cell interference value. The consequence is that the scheduler is unaware of the origin of the interference, thereby making it more difficult to arrive at good scheduling decisions. For managing heterogeneous networks (HetNets), which is a network composed of multiple radio access technologies, architectures, transmission solutions, and radio base stations of varying transmission power, the problem is again that there is no information of the origin of interference, and interference variance, for adjacent cells. This is also caused by the lack of low complexity estimators for these quantities.